Don Stephan
Posts: 825
Joined: 2003-07-18
Location: Cincinnati, Ohio
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Honeycomb and other types of torsion boxes require special interior reinforcement (i.e. solid blocking) to hold screws and fasteners, and in this case isolated supports. It's not possible to add additional point supports at a later time if proven necessary, because the solid blocking won't be present. With the desired design, a torsion box will be very challenging.
MDF is very flat, but does't hold screws and other types of fastener very well. Plywood can have interior voids; if these show up under the pressure of a vacuum press and the veneer power sanded it's possible to sand through the veneer. Neither choice of solid substrate is risk-free.
If you prefer a top only 3/4" thick, I'd probably stay with solid hardwood for overall strength and ability to hold fasteners. But I'd want the three rows of posts (left side, middle, and right) with each row staggered so the board is less likely to split on a row of posts.
If a thicker top is acceptable and there's a strong reason to prefer veneer over solid wood, I'd consider two layers of MDF laminated together if the overall thickness was sufficient for the depth of fastener at the top of the posts, with three rows of support posts. With MDF however (and plywood to a lesser degree), the edges of the veneered top will be likely to be dented with the occasional bump and knock, so I'd probably want to include an edge of oak or maple behind the veneer. But as the top gets thicker, veneer on the (hardwood) edges is more likely to suffer from expansion and contraction of the underlying solid wood.
If the top is for your own personal use, it's easier to try risker designs as long as you're willing to accept the possibility of having to remake the top if it doesn't work. If for someone else I'd be much less likely to take a flyer on a problematic design. Unfortunately, ideal testing would require 6-12 months of actual use.
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